A wireless local area network (WLAN) in the infrastructure basic service set (BSS) mode has an access point (AP) for the BSS, and one or more stations (STAs) associated with the AP. The AP typically has access or interface to a distribution system (DS) or another type of wired or wireless network that carries traffic in and out of the BSS. Traffic to STAs that originates from outside the BSS arrives through the AP and is delivered to the STAs. Traffic originating from STAs to destinations outside the BSS is sent to the AP to be delivered to the respective destinations. Traffic between STAs within the BSS may also be sent through the AP where the source STA sends traffic to the AP and the AP delivers the traffic to the destination STA. Such traffic between STAs within a BSS is really peer-to-peer traffic. The peer-to-peer traffic may be sent directly between the source and destination STAs with a direct link setup (DLS) using an IEEE 802.11e DLS or an IEEE 802.11z tunneled DLS (TDLS). A WLAN in an independent BSS mode (IBSS) has no AP and STAs communicate directly with each other.
In the current IEEE 802.11 infrastructure mode of operation, the AP transmits a beacon on a channel called primary channel. The primary channel is 20 MHz wide and is the operating channel of the BSS. This channel is also used by the STAs to establish a connection with the AP. The channel access mechanism in an 802.11 system is carrier sense multiple access with collision avoidance (CSMA/CA). In this mode of operation, every STA, including the AP, will sense the primary channel and if the channel is detected to be busy, the STA and the AP backs off. Hence one STA (including AP) can transmit at any given time in a given BSS.
In IEEE 802.11n, high throughput (HT) STAs may also use 40 MHz wide channel for communication. This is achieved by combining the primary 20 MHz channel with another adjacent 20 MHz channel to form a 40 MHz wide channel.
In IEEE 802.11ac, very high throughput (VHT) STAs can support 40 MHz, 80 MHz and 160 MHz wide channels. While 40 MHz and 80 MHz channels are formed by combining contiguous 20 MHz channels similar to IEEE 802.11n, 160 MHz channel may be formed either by combining 8 contiguous 20 MHz channels or two non-contiguous 80 MHz channels (80+80 configuration).
The channel operating bandwidth may be reduced for sub 1 GHz modes of operation, which is supported in IEEE 802.11af and IEEE 802.11ah. 802.11af supports 2 MHz, 4 MHz, and 8 MHz bandwidths for operation in TV white space (TVWS). 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths for operation in non-TVWS. Some STAs in 802.11ah are considered to be sensors with limited capabilities, and may support a 1 MHz transmission mode.